Tilt the backbone in the tar pit so it ramps up to the left. Roll jump up to the left towards the lone banana you see floating at the top of the screen and hold the Grab Button to cling to the grassy area. Climb up to the Puzzle Piece.

It's at the bottom of the waterfall to the left of the Tutorial Pig. Ride one of the lower platforms to the very bottom of the screen then grab the Puzzle Piece as you start hopping back up the platforms (it's hard to see but it's slightly to the right of the platforms). This one can be a bit tricky.